Heat stress during reproductive stages remains one of the most critical constraints on rice yield and grain quality, yet progress in developing heat-resilient cultivars is slowed by the complex, polygenic nature of thermotolerance and lengthy breeding cycles. Despite incremental gains through conventional breeding, high temperatures above 35 ºC continue to cause severe spikelet sterility, yield losses, and quality deterioration. The emergence of CRISPR/Cas genome-editing offers a precise and efficient platform to dissect heat-stress mechanisms, and accelerate the development of heat-tolerant rice. CRISPR/Cas9 studies have validated and edited key genes involved in calcium signaling, hormone pathways, reproductive processes, photosynthesis, reactive oxygen species homeostasis, and transcriptional regulation, such as OsCNGC14/16, OsNCED1, OsSPL7, and OsHSP60-3b. Beyond stress resilience, genome editing has improved major yield components, including grain size, panicle architecture, and spikelet number, through targets such as GS3, GW3, Gn1a, and OsSPL16, achieving 28%-40% increases in grain weight and 15%-25% improvements in panicle traits, alongside enhanced grain quality attributes. Remaining challenges, including off-target effects, genotype dependence, limited field validation, and regulatory constraints, are being addressed through high-fidelity Cas variants, optimized sgRNA design, DNA-free editing, and integration with genomic selection and speed breeding. This review synthesizes advances in heat-stress biology and CRISPR/Cas applications in rice, and highlights future opportunities in base and prime editing, transcriptional reprogramming, multiplex genome engineering, and field deployment.
